Polymeric impression molding materials having good dimensional stability

ABSTRACT

1. AN IMPRESSION MATERIAL COMPRISING A COAGULATED MIXTURE OF AN INORGANIC ELECTROLYTE, AT LEAST ONE LATEX EMULSION SELECTED FROM THE GROUP CONSISTING OF NATURAL RUBBER AND SYNTHETIC RUBBER LATICES AND AT LEAST ONE EMULSION SELECTED FROM THE GROUP CONSISTING OF EMULSIONS OF POLYCYCLOPENTADIENE AND A POLYMER IN WHICH CYCLOPENTADIENE IN 1,4- OR 1,2-FORM IS POLYMERIZED TO A SERIES OF FIVE-MEMBER RINGS OF CARBON ATOMS, WITH AN APPROXIMATE MOLECULAR WEIGHT OF ($)(30*,TOLUENE) = 0.1 TO 5.0 AND A HOMOPOLYMER OR COPOLYMER OF VINYL MONOMERS HAVING THE GENERAL FORMULA H2C=C(-R)-X WHEREIN X REPRESENTS A HYDROGEN ATOM, ALKYL GROUP HAVING C1-C20, AN ARYL GROUP, HALOGEN, NITRILE GROUP, CARBOXYL GROUPS CARBOALKOXY GROUP, OR ACYLOXY GROUP, AND R REPRESENTS A HYDROGEN ATOM, ALKYL GROUP HAVING C1-10 OR ALKENYL GROUP HAVING C2-C10, THE AMOUNT OF SAID POLYCYCLOPENTADIENE BEING FROM 10 TO 50 PERCENT BASED ON THE WEIGHT OF LATEX AND THE AMOUNT OF VINYL POLYMER IS 10 TO 50 PERCENT BASED ON THE LATEX.

NOV. 26, 1974 MASATQ K MI ET AL 3,850,870

POLYMERIC IMPRESSION MOLDING MATERIALS HAVING GOOD DIMENSIONAL STABILITY Filed Aug. 30, 1973 FIG. 6

FIG. 7

INVENTORS m I A n un K E AO mWN MA/ AO 0 Kmuu WW WARM ATIOG A M W MRM United States Patent US. Cl. 26029.7 PT Claims ABSTRACT OF THE DISCLOSURE Impression materials prepared by coagulating with an inorganic electrolyte a mixture of at least one latex selected from the group consisting of natural and synthetic rubber latices and at least one emulsion selected from the group consisting of polycyclopentadiene emulsion and vinyl polymer emulsions, and said impression materials which contain a mold releasing agent which is at least one compound selected from the group consisting of liquid paraffin, solid parafiin, squalane, and monoolefinic and diolefinic hydrocarbons.

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of co-pending application Ser. No. 138,570, filed on Apr. 29, 1971, and now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to impression materials of highpolymer emulsions. More particularly, the invention relates to impression materials which are prepared by coagulating with an inorganic electrolyte a mixture of at least one latex selected from the group consisting of natural and synthetic rubber latices and at least one emulsion selected from the group consisting of polycyclopentadiene emulsions and vinyl polymer emulsions, and said impression materials which contain a novel mold releasing agent.

2. Description of the Prior Art Impression materials which have usually been employed by dentists include gypsum plaster, silicone rubber. Thiokol, and sodium alginate. These known materials have the following disadvantages. Gypsum plaster has good shape-holding property (dimensional stability) but, when placed and set in a female mold having a cavity of a larger diameter than the mouth, plaster cannot be taken out without destroying the mold. Also, when impressions of protruding objects are to be taken, plaster may fail to serve the purpose with objects of certain configurations. Silicone rubber is expensive and inconvenient for application because it must be used as a mixture of three different solutions. Thiokol has a very offensive smell and is costly, although it exhibits good shape-holding property. Sodium alginate is excellent in that it is odorless and economical, but its casting undergoes such sharp dimensional change with time that it must be disposed of immediately after the impression-taking.

SUMMARY OF THE INVENTION It is an object of the present invention to provide impression materials which do not have the foregoing disadvantages but are inexpensive and easy to handle.

Another object of the invention is to provide impression materials which possess remarkably good mold releasability in addition to the above-mentioned features.

3,850,870 Patented Nov. 26, 1974 Polymer latices in the form of emulsions are usually destroyed by the addition of an inorganic salt to change them to gels or coagulums. The impression materials according to this invention take advantage of this phenomenon. In the state of a coagulum, a polymer latex requires some elasticity and rigidity because, after the removal of the mold with intricate configurations, it has to reproduce the original configurations of the mold.

A material which satisfies the above requirements to a large measure is a highly concentrated styrene butadiene rubber latex (e.g., goods name of Japan Synthetic Rubber Co., Ltd.; JSR#0561). This SBR latex can provide an impression material when it is half coagulated with calcium sulfate, allowed to set in a mold for minutes, and freed of the mold. However, when used as an impression material, the latex displays somewhat inadequate dimensional stability with time due to shrinkage and, in order to reproduce the mold configurations, it must be treated within two hours after the impression-taking. (Refer to Referential Examples 1 to 5.)

It has now been found that, when a latex mixture prepared by adding a suitable amount of at least one substance from the group consisting of polycyclopentadiene emulsion and vinyl polymer emulsions to a natural rubber latex or synthetic rubber latex such as SBR latex, the resulting casting undergoes very little dimensional change with time and remains dimensionally stable for more than 16 hours. The present invention is based on this discovery.

The present invention thus provides impression materials which are prepared by coagulating with an inorganic electrolyte a mixture of at least one material selected from the group consisting of natural rubber and synthetic rubber latices (emulsions), and a polycyclopentadiene emulsion.

Also the present invention provides impression materials which are prepared by coagulating with an inorganic electrolyte a mixture of at least one material selected from the group consisting of natural rubber and synthetic rubber latices (emulsions), and an emulsion of a homopolymer or copolymer of vinyl monomers having the general formula wherein X represents a hydrogen atom, an alkyl group having C -C an aryl group, advantageously a nucleus selected from the group consisting of the phenyl series, e.g., phenyl, a halogen atom, a nitrile group, a carboxyl group, a carboalkoxy group or an. acyloxy group, and R represents a hydrogen atom, an alkyl group having C -C or an alkenyl group having C C The impression molds formed of the aforementioned high-polymer latex impression materials have most satisfactory reproducibility in dimensions and otherwise. However, if the shape to be cast is made of a material highly aifinitive to any latex component of the particular impression material, for example, a synthetic high polymer, such as, polymethyl methacrylate to constitute artificial teeth, the impression mold may partly adhere to the shape to be cast, thus producing some indentations or irregularities on the resultant surface. In extremecases the impression mold is partly torn off and the impression material fails to serve properly. Such cases, however, are not rare.

In view of the foregoing, we made diversified investigations and have found that, if liquid paraffin, solid paraffin, squalane, or a monoolefinic or diolefinic hydrocarbon is emulsified with a surface active agent and a small amount of the resulting emulsion is added, the mold releasing property of our impression materials can be surprisingly improved without any unfavorable eifect upon the inherent features of the materials, such as shrinkage resistance, fluidity, pliability, setting time, and strength after setting. This discovery has led to the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a container for impression material;

FIG. 2 is a bottom view of the container of FIG. 1;

FIG. 3 is a perspective view of an impression mold;

FIG. 4 is a perspective view of a reproduced mold;

FIG. 5 is a front view of another form of impression mold;

FIG. 6 is a bottom view of the mold of FIG. 5;

FIG. 7 is a side view of the mold of FIG. 5; and

FIG. 8 is a perspective view of a reproduced mold obtained from another form of impression mold.

DESCRIPTION OF THE PREFERRED EMBODIMENT Thus, the present invention provides impression materials which are prepared by coagulating in an inorganic electrolyte a mixture of at least a member of the group consisting of natural rubber and synthetic rubber latices (emulsions), at least a member of the group selected from the group consisting of polycyclopentadiene emulsion and vinyl polymer emulsions, and at least a member of the group consisting of liquid parafiin, solid paraffin, squalane, and monoolefinic and diolefinic hydrocarbons. In the practice of the present invention, synthetic rubbers which may be used include styrene-butadiene rubber (SBR), polybutadiene (BR), polyisoprene (IR), acrylonitrilebutadiene rubber (NBR), isobutylene-isoprene rubber (IIB), ethylene-propylene-diene rubber (EPR), and acrylic rubber. Suitable polycyclopentadiene is a polymer of cyclopentadiene in 1,4- or 1,2 form polymerized to a series of five-member carbon rings, with a molecular weight of approximately The suitable combined concentration of a ruber latex and polycyclopentadiene emulsion ranges from 60 to 90 percent, preferably from 65 to 85 percent, on a dry weight basis. The proportion of the polycyclopentadiene emulsion which is sufiicient for achieving its purpose is between 10 and 50 percent, preferably between and percent, on the basis of the weight of the mixture of the rubber latex and polycyclopentadiene emulsion.

Among the homopolymers and copolymers which may be employed for the present invention are, for example, polyolefins, polystyrene, poly-ot-methyl styrene, polyvinyl chloride, polyacrylonitrile, polyacrylic acid esters, polymethyl methacrylate, polyvinyl acetate, styrene-butadiene copolymer (with a styrene content of over percent by weight), acrylonitrile-styrene copolymer, and acrylo nitrile-butadiene-styrene resin. Polystyrene, polymethyl methacrylate and styrene-butadiene copolymer are particularly desirable.

Suitable combined concentrations of a rubber latex and vinyl polymer emulsions to be used in the present invent1on are between and 90 percent, and preferably between and percent, on the basis of total solid content (TSC) weight.

The mixing ratio of natural rubber or synthetic rubber to a vinyl polymer may suitably range from -50 percent rubber latex to 10-15 percent vinyl polymer emulsion.

Useful dispersion stabilizers for the mixture of a rubber latex and polycyclopentadiene emulsion or vinyl polymer emulsion are salts of fatty acids, alkylbenzene sulfonic acids, sulfuric esters of higher alcohols, and alkylsulfonic acids. Inorganic electrolytes as coagulants may include gypsum, magnesium sulfate, aluminum sulfate, iron sulfate, sodium silicofiuoride, and alum. These may be used either singly or in combination. Generally, such an inorganic electrolyte may be used in an amount ranging from 1 to 50 percent, preferably from 1 to 25 percent, on the basis of the weight of the polymer latex.

The impression materials of the present invention form molds which are dimensionally stable for many hours as above described. When impression molds are to be made in a lot of tens or hundreds at one time, it is only necessary to form a master mold and then reproduce it as with gypsum. This permits remarkable improvements in working efficiency and operation procedure. Moreover, it offers an additional advantage of great ease of operation in that the impression-taking and mold processing can be performed in different places.

The liquid paraffin, solid paraffin, squalane, or monoolefinic or diolefinic hydrocarbon which may be used as a mold releasing agent preferably has from 10 to 200 carbon atoms and a boiling point of over C. Whether of straight chain or branched, the structure has no adverse eifect upon the mold releasing property. The amount of the compound which is used as a mold releasing agent is suitably between 0.5 and 10 percent, preferably between 1 and 3 percent, on the basis of the dry weight of the latex.

Heretofore, silicone resin, solid wax and the like have been employed as mold releasing agents. They are not mixed in impression materials but applied on the objects of impression so that the impressions can be taken using the impression materials. The mold releasing agent according to the present invention, by contrast, is mixed beforehand in an impression material and, therefore, the object to be impressed needs no pretreatment at all. Immediately after the object of impression is cleaned, the impression is taken using the impression material. Then, the mold releasing agent in the impression material acts by itself to faciltate the mold releasing, and an impression mold having very smooth surface is produced. In other words, the present invention has an amazing advantage of omitting the step of applying a mold lubricant to the object of impression.

The impression materials according to the present invention may also contain, if necessary, a filler, such as, calcium carbonate, talc or diatomaceous earth, and/or a viscosity-increasing agent, such as, sodium alginate, potassium alginate, polyacrylate or carboxymethylcellulose and/or a pH controlling agent (setting-rate-adjusting agent), such as, sodium pyrophosphate, potassium pyro phosphate, sodium carbonate or potassium carbonate.

The present invention will be more fully described below with reference to the accompanying drawing and in connection with the following examples which are not in any way restrictive and also with referential examples, in which all parts and percentages are by weight.

REFERENTIAL EXAMPLES 1 TO 5 (A) Preparation of master latex Parts SBR latex (JSR #0561) 100 Sodium alginate 0.5 Sodium pyrophosphate 0.5 Calcium carbonate 10 Total 111.0

These were thoroughly mixed up and the mixture was allowed to stand for not less than one full day. (A suitable amount of an alcoholic solution of phenol phthalein may be added as a colorant.)

(B) Use as impression material (a) Preparation of impression material and impressiontaking:

Parts Master latex 100 fi-Gypsum 15 These were thoroughly mixed up for one minute, and the mixture was poured before setting into a cylindrical impression material container 2, as shown in FIG. 1, having perforations 1 which were 1.2, in diameter.

Mold Exam- Examdimen plc 9 ple 10 sions Example- Example- VINYL ACETATE Referential example VINYL CHLORIDE Referential example Referential example 1 are shown in Table 4. In these examples the standing time was zero.

TABLE 4.-WHERE SBR LATEX WAS USED WITH POLY- 11 (mm.) (mm.)

EXAMPLES 11 TO 15 As the vinyl polymer, polyvinyl chloride in the form 20 of an emulsion (TSC 69%) was employed. The results (percent) ll J SR #0561 (percent) Dimension:

a (mm). b (mm.)

EXAMPLES 16 TO 20 As the vinyl polymer, a polymethyl methacrylate (MMA) emulsion (TSC 65%) was used. The results are ture of the latex and a polycyclopentadiene emulsion 40 given in Table 6. The standing time was zero as in Exam- (percent) JSR #0561 (percent) Dimension:

TABLE 6.WHERE SBR LATEX WAS USED WITH POLY'MMA.

are given in Table 5. The standing time was zero in Examples 9 and 10.

TABLE 5.-WHERE SBR LATEX WAS USED WITH POLY- manner as in Referential Examples 1 to 5. The results Polyvinyl acetate emulsion (per- Dimension:

Polyvinyl chloride emulsion ples 9 and 10.

Poly-MMA emulsion Parts B-Gypsurn 100 Water 30 These were thoroughly mixed up, and the mixture was poured into the mold of impression material with vibration by a vibrator. The mixture was allowed to stand at room temperature 20 C. for 20 minutes for setting. Thereafter, a mold (as shown in FIG. 4) which had been reproduced with gypsum was taken out.

mold dimen- SlOl'lS mm. in height. As shown in FIG. 2, it also has perforations 1 at the bottom 3. Next, an impression mold as shown in FIG. 3 (measurements: a=7.0 mm., b: 2.3 mm, and c=6.0 mm.) was forced into the container and kept as it was for 5 minutes at room temperature. After setting of the impression material, the impression mold was removed.

material:

As a criterion for measurement of dimensional stability, impressions were taken with an impression matesum, and the dimensions of the molds reproduced with gypsum were measured. The results are shown in Table 1.

TABLE I Actual 30 Relerenttal example- EXAMPLES 1 TO 3 As the master latex, not SBR latex alone but a mix- TABLE 2 Referential Actual example (with a solid content of 80 percent) was used in the impression-taking in the same manner as described in Referential Examples 1 to 5. The data are given in Table 2 (in which case, however, the standing time is zero).

The container was 12.5 mm. in inside diameter and 15 (b) Reproduction with gypsum from mold of impression rial in conformity with the procedure (a) above, and the impression molds were removed, and allowed to stand for different periods of time at room temperature before the impression molds were reproduced with gypmm mm mm mm mold size

Exam- Exam- Exam- 1 ple 1 ple 2 ple 3 CPD emulsion* (per- Example Actual Polystyrene emulsion EXAMPLES 4 TO 8 As the master latex, a mixed latex of 75 percent JSR #0561 and 25 percent polycylopentadiene emulsion was used and the standing time was varied following the impression-taking as in Referential Examples 1 to 5, and the reproducibility with gypsum was observed. The results are given in Table 3.

TABLE 3 Example- (percent) JSR #0561 (percent). Dimension:

EXAMPLES 26 TO 30 mold size EXAMPLES 9 AND 10 As the master latex, as mixture of SBR latex and polywas used, rather than Standing time (hours).

vinyl acetate emulsion (TSC 61% the SBR latex alone, for impression-taking in t mensions were examined in the same manner as described in Referential Examples 1 to 5. The results were as given in Table 8.

TABLE 8.TIME DEPENDENCY OF POLY-MMA- CONTAINING IMPRESSION MATERIAL As the master latex, a mixture of 75 percent JSR #0561 and 25 percent polystyrene emulsion was used, and the time dependency and reproducibility of mold dimensions were examined in the same manner as described in Referential Examples 1 to 5. Table 9 shows the results.

TABLE 9.TIME DEPENDENOY OF POLYSTYRENE- CONTAINING IMPRESSION MATERIAL Example- Standing time (hours) 1.5 3.0 6.0 16.0 Dimenslon:

a(mm.) b(mm.)

EXAMPLES 36 TO 40 As the master latex, a mixture of 80 percent J SR #0561 and percent high-styrene latex (combined styrene 85%, TSC 66.8%) was used, and the time dependency and reproducibility of mold dimensions were examined in the same manner as in Referential Examples 1 to 5. The results are given in Table 10.

TABLE 10.-TIME DEPENDENCY OF HIGH-STYRENE LATEXEONTAINING IMPRE SSION MATERIAL Example- Standing time (hours) 0 1. 5 3. 0 6. 0 16. 0 Dimension:

EXAMPLES 41 TO 46 TABLE 11.EFFECTS OF DIFFERENT PROPORTIONS OF ABS RESIN ON PERFORMANCE OF IMPRESSION MATERIAL Referential Examp1e example ABS resin emulsion (percent) 0 10 25 JSR 0561 (percent) 100 90 75 60 Dimension:

TABLE 12.TIME DEPENDENCY OF ABS RESIN- CONTAINING IMPRESSION MATERIAL Exampler 44 45 40 0 Standing time (hours) 0 6 16 Dimension:

1 REFERENTIAL EXAMPLES 6 TO 10 (A) Preparation of master latex Parts NR latex 100 Sodium alginate 0.5 20 Sodium pyrophosphate 0.5 Calcium carbonate 10 Total 111.0

These were thoroughly mixed up, and the mxiture was allowed to stand for more than one full day.

(B) Manufacture of impression material and impression- 30 taking (This process was worked out as same as Referential Examples 1 to 5) (C) Reproduction of impression material mold with gypsum (This process Was worked out as same as Referential Examples 1 to 5) As a criterion for determination of dimensional stability, the period of standing time at room temperature required between the removal of the impression mold following the impression-taking with the particular impression material (B) and the reproduction of the impression mold with gypsum was varied and the dimensions of the gypsum reproduction were measured. The results are given in Table 13.

TABLE 13 Actual Referential examplemold dimen- 6 7 8 9 10 sions Standing time (hours). 0 1.5 3.0 6.0 16 0 Demension:

0 (mm) 7.15 7.20 7 20 7.40 7 40 7.00 b(m.m.) 2.35 2.30 235 2.4.0 2 40 2.30 50 C(mm.) 0.20 e 30 6 50 6.60 0 70 6.00

EXAMPLES 47 to 74 As master latices, NR (natural rubber), IR, NBR and IIR latices were used respectively in mixture with emulsions of polycyclopentadiene, polystyrene, ABS resin and polymethyl methacrylate (PMMA) (TSC 6169%). After impression-taking with these compositions in the manner as described in Referential Examples 6 to 10, the moldings were examined or their dimensional stability. The results are shown in Tables 14 and 15. Table 14 shows the dimensional changes of the products formed of the combinations of NR, IR, IIR and NBR latices and the various resin emulsions. Throughout these examples, the standing time was set at naught. Table 15 indicates the changes with time recorded when the mixtures of NR With 8% Liquid Paratfin n the Basis of the Latex With 2% Undeeene on the Basis of the Latex Example No.- Example No.-

Standing time (hours) 0 6 16 Standing time (hours) 0 6 16 Dimensions: Dimensions:

7. 00 7.00 7. 05 7.00 7.05 7.00 2. 30 2.30 2. 30 2. 30 2. 30 2. 30 6. 00 6. 00 6. 00 6. 00 6. 00 6. 05 With 4% Liquid Parafiin on the Basis of the Latex 10 With 5% Undecene on the Basis of the Latex Example No.- Example No.-

' 6 Standing time (hours) 0 6 16 ggg (hours) 0 10 Dimensions; 15 7. 05 7. 31 (I (111111.) 7. 00 7. 0O 7. O0 2 3O 2 00 b (m)... 2. 25 2. 25 2. 30 05 1 0 (mm.) 6.00 6.00 6.05

. With 8% Undecene on the Basis of the Latex With 5% Liquid Paraffin on the Basis of the Latex Example N Example N o. 37 38 39 16 17 8 Standing time (hours) 0 6 16 Dimensions: Standing time (hours) 0 6 7. 05 7. 05 7. 10 Dimensions: 2. 30 2. 35 2. 35 7. 00 7.00 7. 00 6.05 6.10 6.10 2. 30 2.30 2. 30 6.00 6.00 6.00 EXAMPLE 76 With 8% Liquid Paraniii on the Basis of the Latex Generally in accordance with Example 75, tests were Example N0 conducted with a master latex with or without the addition of a mold releasing agent. As the impression mold, the 19 20 21 One illustrated in FIGS. 5 to 7 was employed. The mold Standing time (hours) 0 e is releasing conditions observed are compared in Table 18. 1 2 3? 7 05 7 05 7 05 The material of the reproduced mold (FIG. 8) was polyb 1): n 2135 2:35 2:30 methyl methacrylate. In this example, the impression mold (1mm shown in FIGS. 5 to 7 was used, because the impression With 10% Liquid Parafiin on the Basis of the Latex mold of FIG. 3 is not pointed at the lower end and hardly Example N0 shows the difference between the composition which contains a mold releasing agent and the composition which 22 23 24 does not.

Standing time (hours) 0 6 16 (A) Master latex (TSC 65%) Without mold releasing Dimensions: nt

7.05 7.05 7.05 age 2. 35 2. a0 2. 35 Parts 6. 10 6.10 6. 10 TABLE 17.-CHANGES WITH TIME (WITH A MOLD RELEAS- JSR #0601 20 ING AGENT OF UNDECENE) Sodium pyrophosphate 2.0 With 0.5% Undecene on the Basis of the Latex S nmi alginate 2.0 Exam M No Calcium carbonate 10.0 p Phenol phthalein 0.1 25 26 27 Standing time (hours) 0 6 1 al 114.1 Dlmenswns' g8 7'00 100 (B) Master latex (TSC with mold releasing agent 2. 30 2. 30 Parts 6.00 6. 00 6.05

JSR #0561 With 1% Undecene on the Basis of the Latex JSR #0601 20 Example No.- r Sodium pyrophosphate 2.0 0 Sodium alginate 2.0 28 29 30 I Calcium carbonate 10.0 g i 1116 (hours) 0 6 16 Ph l hth l i Q 1 11118118101181 Mold releasing agent (as liquid paraffin) 2.0 2. 30 2. 30 2. 30 6-00 6.00 6.00 60 Total 1161 TABLE 18 Condition Impression Testing stage material Best (1) Kneading on rubber ball milL..-

container.

Master latex (A) Master latex (B) Master latex (B)..

(3) Insertion of impression mold.. Master latex (A).

I Master latex (B) (4) Withdrawal of impression mold" Master latex (A) ..I No good Master latex (B) East to carry I (5) Appearance of reproduced mold- Master latex (A) Fairly precise... Lacks fineness.

Master latex (B) Precise and fine The impression mold is diflieult to remove. The surface oi the impressed mold is not completely and cleanly exposed.

What is claimed is:

1. An impression material comprising a coagulated mixture of an inorganic electrolyte, at least one latex emulsion selected from the group consisting of natural rubber and synthetic rubber latices and at least one emulsion selected from the group consisting of emulsions of polycyclopentadiene and a polymer in which cyclopentadiene in 1,4- or 1,2-form is polymerized to a series of five-member rings of carbon atoms, with an approximate molecular weight of [n]t2.'....=0.1 to 5.0

and a homopolymer or copolymer of vinyl monomers having the general formula R H2 C=(|3X wherein X represents a hydrogen atom, alkyl group having C C an aryl group, halogen, nitrile group, carboxyl group, carboalkoxy group, or acyloxy group, and R represents a hydrogen atom, alkyl group having C C or alkenyl group having C C10, the amount of said polycyclopentadiene being from to 50 percent based on the weight of latex and the amount of vinyl polymer is 10 to 50 percent based on the latex.

2. The impression material of claim 1 which funther comprises at least one compound in emulsified form selected from the group consisting of liquid paraffin, solid parafiin, squalane, and monoolefinic and diolefinic hydrocarbons.

3. An impression material according to claim 1 wherein the homopolymer or copolymer of vinyl monomers is a polyolefin, polystyrene, poly-a-methyl styrene, polyvinyl chloride, polyacrylonitrile, polyacrylic acid, polymethyl methacrylate, polwinyl acetate, styrene-butadiene copolymer with a styrene content of over 50 percent by weight, acrylonitrile-styrene copolymer, or acrylonitrile-butadienestyrene resin.

4. An impression material according to claim 1 wherein the inorganic electrolyte is at least one compound selected trom the group consisting of gypsum, magnesium sulfate, aluminum sulfate, iron sulfate, sodium silicofiuoride, and alum.

5. An impression material according to claim 2 wherein the liquid parafiin, solid paraffin, squalane, and monoolefinic and diolefinic hydrocarbons have from 10 to 200 carbon atoms in the molecule and having boiling points of not lower than 100 C.

6. An impression material as. claimed in claim 1, wherein said aryl group is a nucleus selected from the phenyl series.

7. An impression material as claimed in claim 6, wherein said nucleus is phenyl.

8. A process for preparing the impression materials of claim 1 which comprises the steps of mixing at least one latex emulsion selected from the group consisting of natural rubber and synthetic rubber latices and at least one emulsion selected from the group consisting of emulsions of polycyclopentadiene and vinyl polymers, and then coagulating said mixture with an inorganic electrolyte.

9. A process for preparing impression materials of claim 2 which comprises the steps of mixing at least one latex emulsion selected from the group consisting of natural rubber and synthetic rubber latices, at least one emulsion selected from the group consisting of emulsions of polycyclopentadiene and vinyl polymers, and at least one compound selected from the group consisting of liquid paraffin, solid parafiin, squalane, and monoolefinic and diolefinic hydrocarbons, and then coagulating said mixture with an inorganic electrolyte.

10. An impression material according to claim 1 wherein the synthetic rubber latex is at least one latex selected from the latices of styrene-butadiene rubber, polybutadiene, polyisoprene, acrylonitrile-butadiene rubber, isobutylene-isoprene rubber, ethylene-propylene rubber, and acrylic rubber.

References Cited UNITED STATES PATENTS 3,103,498 9/1963 Scriba 260-894 3,145,189 8/1964 Fourier 260-894 3,513,227 5/1970 Coene et al 260-892 3,620,778 11/1971 Morrell 106-35 FOREIGN PATENTS 1,219,339 1/1971 Great Britain 106-35 MELVIN GOLDSTEIN, Primary Examiner E. WOODBERRY, Assistant Examiner US. Cl. X.R.

260-17, 17.4 ST, BB, 5, 29.7 GP, 29.7 R, 33.6 UA, 889, 890, 892, 893, 894 

1. AN IMPRESSION MATERIAL COMPRISING A COAGULATED MIXTURE OF AN INORGANIC ELECTROLYTE, AT LEAST ONE LATEX EMULSION SELECTED FROM THE GROUP CONSISTING OF NATURAL RUBBER AND SYNTHETIC RUBBER LATICES AND AT LEAST ONE EMULSION SELECTED FROM THE GROUP CONSISTING OF EMULSIONS OF POLYCYCLOPENTADIENE AND A POLYMER IN WHICH CYCLOPENTADIENE IN 1,4- OR 1,2-FORM IS POLYMERIZED TO A SERIES OF FIVE-MEMBER RINGS OF CARBON ATOMS, WITH AN APPROXIMATE MOLECULAR WEIGHT OF ($)(30*,TOLUENE) = 0.1 TO 5.0 AND A HOMOPOLYMER OR COPOLYMER OF VINYL MONOMERS HAVING THE GENERAL FORMULA H2C=C(-R)-X WHEREIN X REPRESENTS A HYDROGEN ATOM, ALKYL GROUP HAVING C1-C20, AN ARYL GROUP, HALOGEN, NITRILE GROUP, CARBOXYL GROUPS CARBOALKOXY GROUP, OR ACYLOXY GROUP, AND R REPRESENTS A HYDROGEN ATOM, ALKYL GROUP HAVING C1-10 OR ALKENYL GROUP HAVING C2-C10, THE AMOUNT OF SAID POLYCYCLOPENTADIENE BEING FROM 10 TO 50 PERCENT BASED ON THE WEIGHT OF LATEX AND THE AMOUNT OF VINYL POLYMER IS 10 TO 50 PERCENT BASED ON THE LATEX. 